Although the presence of tumor-specific or tumor-associated antigens and other markers of malignancy have been demonstrated on a number of solid tumors in syngeneic animals, their occurrences on human leukemic cells is controversial due to the recent finding of DR or IA-like alloantigens on malignant and normal leukocytes. Chronic lymphocytic leukemia (CLL) is a malignancy of monoclonal origin in the B-lymphocyte lineage with a restricted phenotype and suitable for a comparative immunochemical analysis to their normal cellular counterparts. We have preliminary evidence indicating that CLL cells possess a tumor-associated antigen distinct from any known alloantigen; this CLL antigen cannot be detected on normal T or B lymphocytes or on cells from other forms of myelocytic or lymphocytic leukemia. However, more conclusive proof of the uniqueness of the tumor-associated antigen requires the isolation of the component from plasma membranes and detailed structural characterization. The purpose of this project will be to first further substantiate the nature of the specificity of the tumor-associated antigen using a 51Cr-microcytotoxicity assay, an immunofluorescent technique, and blocking the stimulator B-cells with antibody in the mixed lymphocyte reaction to allogeneic lymphocytes. Subsequently, 125I-labeled plasma membranes from CLL cells will be solubilized in NP-40 detergent and the tumor-associated antigen will be isolated on an immunoabsorbent column consisting of AH-Sepharose with covalently attached tumor-specific antibody. If this proves successful, a detailed biochemical characterization, including molecular weight determinations, amino terminal analyses, carbohydrate composition will be performed. Also, antibody will be produced to the isolated component and a radioimmunoassay will be established to measure the presence of the tumor antigen or antibody in CLL patients. Finally, attempts will be made to generate monoclonal antibody from mouse x mouse hybridomas, which will allow the production of specific antibody in large quantities to a) provide a specific immunoassay for quantifying malignant cells in the peripheral blood of patients, b) isolate and structurally characterize the antigen, and c) evaluate the effectiveness of the antibody in vivo in eradicating the tumor. The identification and isolation of this antigen could have important and immediate clinical applications.